The invention relates to an apparatus, system, and method for degassification of a fiberous suspension, particularly a medium consistency (i.e., about 6 to 15%) pulp. In many operations relating to the production and transfer of paper pulp, gases are introduced into the fiberous suspension. The gases become entrained in the pulp and form an emulsion, and can present difficulties in the subsequent processing of the pulp, such as the washing, pumping, and bleaching thereof. According to the present invention, the adverse effects of gases emulsified in pulp may be avoided by removing the gases from the pulp in a simple and effective manner by imparting high speed velocity components to the pulp and passing with a whirling motion in a decreasing diameter circular, axial path.
Heretofore, it has been known to impart a whirling motion to pulp for various purposes. For instance U.S. Pat. No. 3,313,413 teaches a separation of dirt particles and like undesirable solid materials, along with air bubbles, from pulp to clean the pulp. Further, as taught by U.S. Pat. No. 4,093,506, it is known to utilize a blade assembly to impart a high speed rotational movement to pulp while introducing liquids to be mixed therein to provide fluidization of the pulp and thus effective mixing of the components. Also, it is known from U.S. Pat. No. 3,771,290 to de-aerate a flowing liquid, such as water, by imparting a whirling action thereto. However heretofore an effective mechanism for degassification medium consistency (i.e., about 6 to 15%) pulp has not been utilized.
According to the present invention the degassification of medium consistency pulp is accomplished in a simple and effective manner. A pulp degassifier is provided which includes the following elements: A housing substantially circular in cross-section and tapering inwardly from a first end thereof toward a second end thereof along a central axis. Means defining a pulp inlet to the housing adjacent the first end thereof, the pulp inlet extending along a line intersecting a plane containing the central axis (e.g., the pulp inlet is tangential). Means defining a pulp outlet adjacent the second end of the housing, the pulp preferably being concentric with the central axis. A blade assembly, and means for mounting the blade assembly adjacent the pulp inlet for rotation about an axis generally coincident with the housing central axis, and means for rotating the blade assembly about the axis so that the blade assembly imparts a high velocity to the pulp. Means defining a gas outlet adjacent the housing first end and adjacent the central axis; and means for preventing short-circuiting of pulp from the pulp inlet to the gas outlet.
The blade assembly includes blades having tapered radially-outwardmost edges thereof parallel to the taper of the housing, and the pulp inlet includes a pipe having a terminating end with the same taper and terminating in close proximity to the blades radially-outwardmost edges. The short-circuiting preventing means comprises a conical tube also having a taper corresponding substantially to the housing taper, and the radially-inwardmost edges of the blades preferably also have the same taper and overlap the conical tube in the axial direction. Preferably the means mounting the blade assembly for rotation comprises a shaft passing through an end cap at the housing first end, and the gas outlet comprises a plurality of openings in the end cap surrounding the shaft.
A degassifier according to the present invention preferably comprises part of a pulp treating system, and may be mounted atop a pulp treatment vessel. For instance, a degassifier according to the present invention would ideally be mounted on top of an oxygen reactor blow tank, gases being vented upwardly from the degassifier and the degassified pulp being discharged downwardly into the blow tank.
Utilizing the degassifier it is possible to effectively degassify pulp having a consistency of about 6 to 15%. The pulp is fed into the housing through the pulp inlet with a velocity component intersecting a plane containing the central axis of the housing (e.g., tangentially). The blade assembly is rotated to impart a high speed rotational velocity component to the pulp as it enters the housing. Movement of the pulp along the central axis of the housing toward the pulp outlet is effected while the gas within the pulp is being squeezed out. Gas separated from the pulp is withdrawn through the gas outlet adjacent the central axis and pulp inlet of the housing, and may be discharged into the atmosphere or may be treated to remove certain components thereof before discharge.
It is the primary object of the present invention to provide a simple and effective means for degassifying medium consistency paper pulp or the like. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.